Greater food availability reduces tarsus asymmetry in nestling Blue Tits

Previous work has shown that the quantity or quality of food affects the degree of asymmetry in bilateral body traits in adult birds, but so far there is no evidence that this is the case in early phases of growth too. I studied asymmetry of tarsus length Of nestling Blue Tits (Parus caeruleus) in relation to supplemental feeding. I offered food, in the form of meal-worms (Tenebrio molitor) and wax moth (Galleria mellonella) larvae, to the adults during the brood-rearing period. The parents consumed the extra food themselves and fed the brood an amount corresponding to one-third of the brood's total food intake. Food supplementation resulted in reduced asymmetry of nestling tarsus length, indicating that body asymmetry in early phases of life, not only in adult birds, depends on energy or protein intake.